This invention relates to systems having plural signal-carrying channels, such as scanning arrays, and, more particularly, to a method and apparatus for fault testing of components in and for measuring and adjusting starting phase of the array prior to a scan to form a focused beam.
Plural channel systems are often constructed with numerous signal-carrying channels arranged in parallel. Examples of such systems are found in electrical communication, including telemetry in which different messages are transmitted along parallel channels, apparatus for sound amplification and recording wherein a signal is divided among separate spectral passbands for correction of a loudness characteristic, and array antennas wherein multiple channels provide various time delays and/or phase shifts for steering a beam of radiation.
In any of the foregoing plural channel systems, optimum operation of the system is obtained when the design characteristics of the respective channels are maintained. Such characteristics may include preset time delays, preset phase shifts, and preset amplification factors for signals propagating through the channels. A calibration process and equipment are utilized to provide optimum operation.
One area of considerable interest occurs in a microwave landing system (MLS) utilized for guiding aircraft to a landing on an airport runway. An array antenna is advantageously employed in an MLS for forming a glide slope beam or a localizer beam. The direction and the pattern of the beam are dependent on the phase shifts (and possibly on amplitude shading factors) applied to radiators of the array by individual signal-carrying channels coupled to respective ones of the radiators. MLS phase calibration is employed to measure the insertion phase of each channel of an MLS array. The calibration information is used to adjust the starting phase of each element in the array to compensate for the insertion phase errors resulting from manufacturing processes, tolerances and component aging. Proper MLS phase calibration results in a well-focused beam with low side lobes and should be performed periodically to correct aging effects. Calibration of the array antenna is important to insure that the beam is properly formed and correctly directed for a safe landing by the aircraft.
A problem arises in that the calibration of the foregoing systems has entailed overly complex equipment and time consuming processes. For example, in the case of a phased array antenna, such processes have employed the injection of test signals followed by the measurement of in-phase and quadrature components utilizing complex algorithms in computers. This problem is due, in part, to the difficulty of measuring one channel without being "swamped" by all other channels in the array.